Collagen is a protein included in the dermis, ligament, tendon, bone, cartilage, and the like, and is a main component of extracellular matrices of multicellular organisms. Advances in research have revealed that collagen has various physiological functions. There is still ongoing research for discovery of new physiological functions and new uses of collagen molecules.
Research has so far revealed that a single collagen molecule is made up of three polypeptide chains, which form a helical structure to constitute a collagen molecule.
That domain of each polypeptide chain which forms a helical structure is called triple helical domain, which has a characteristic amino acid sequence. Specifically, the triple helical domain has repeated occurrences of an amino acid sequence represented as “Gly-X-Y”. In this amino acid sequence, which is made up of three amino acids, the amino acids other than glycine (namely, X and Y) may each be any of various amino acids.
A collagen molecule has a telopeptide(s) at the amino terminus and/or carboxyl terminus thereof (stated differently, at the amino terminus and/or carboxyl terminus of each polypeptide chain included in the collagen molecule), the telopeptide serving as a main antigen site of collagen. The telopeptide(s) is present in a polypeptide chain in the collagen molecule, outside the above-described triple helical domain and close to the amino terminus or carboxyl terminus.
Treating collagen with an enzyme such as a protease to partially remove telopeptides from the collagen molecules is known to reduce the antigenicity of the collagen molecules to a low level. Such a collagen molecule with a telopeptide(s) partially removed is called an atelocollagen.
Research has so far revealed that collagen, atelocollagen, and a product of degradation of collagen or atelocollagen with a protease each have various physiological functions. There have been developed various uses of collagen, atelocollagen, and a product of degradation of collagen or atelocollagen with a protease on the basis of their physiological functions (see, for example, Patent Literatures 1 and 2).
Patent Literature 1 discloses a technique that allows a degradation product resulting from treating collagen or atelocollagen with a protease (for example, pepsin or actinidain) to be used as a hemostatic medical material. Further specifically, Patent Literature 1 discloses a technique of first treating a skin of a yellowfin tuna with pepsin to obtain an aqueous solution containing atelocollagen and then adding sodium chloride to that aqueous solution to precipitate and recover the atelocollagen. When the atelocollagen is recovered as a precipitate, the sodium chloride is removed together with the supernatant. The technique of Patent Literature 1 next degrades the atelocollagen, recovered as a precipitate, with actinidain to produce a degradation product, so that the degradation product is used as a hemostatic medical material.
Patent Literature 2 discloses a technique that allows a degradation product resulting from treating collagen or atelocollagen with a protease to be used as a composition for prevention or therapy of arteriosclerosis and diseases attributed to arteriosclerosis. Further specifically, Patent Literature 2 discloses a technique that allows a degradation product of collagen which degradation product results from degrading, with a protease, collagen with minerals removed therefrom to be used as a composition for prevention or therapy of arteriosclerosis and diseases attributed to arteriosclerosis.
In a case where collagen or atelocollagen is degraded with a protease as described above, such collagen or atelocollagen is typically degraded under a condition of a low salt concentration. In the case where collagen or atelocollagen has been degraded under such a condition of a low salt concentration, amino acid sequences of the degraded collagen and atelocollagen have already been identified, which are disclosed in, for example, Non Patent Literature 1.